JPS5833266A - Electrophotographic copying machine - Google Patents

Abstract

PURPOSE:To obtain an electrophotographic copying machine which is capable of expanding the density variable width of a line image, and also adjusting the copied image density in a state that a density variation of the line image and a density variation of a solid image are kept almost constant. CONSTITUTION:A controlling circuit 10 for executing adjustment of picture density controls the charged potential on a photosensitive drum and also controls the developing bias potential, and the applied potential of the developing bias is secided so as to satisfying the relation of VBVo-200V (VB: developing bias potential, Vo: photosensitive body charged potential) in accordance with the charged potential of the photosensitive drum fed back by said detector 4. The charged potential on the photosensitive drum 1, which is adjusted in this way and is provided by a charger 2 is detected by the detector 4, and the developing bias of a potential value decided in accordance with said expression in the controlling circuit 10 is applied to a developing sleeve 8 from an electric power supply 9. That is to say, if the charged potential is 450V, the developing bias potential is adjusted to 250V, and if the former potential is 350V and 250V, the latter potential is adjusted to 100V and 50V, respectively, and absolute value of the potential difference between the charged potential and the developing bias potential is held at 200V.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to an electrophotographic copying machine, and particularly to an improvement in an image density control section thereof.

Conventional Hulling Methods Conventionally, in electrophotographic copying machines, laser beam printers, etc., methods for adjusting the density of a copied image include: (1) A method of varying the rotational speed of the developing sleeve or the rotating speed of the magnetic developing roll ( 2) A method is known in which the potential of the developing bias, that is, the potential applied to the developing electrode is made variable.

However, in method (1), even if the rotation speed of the developing sleeve or magnetic developing roll is varied, a sufficient range of variation in the density of the copied image cannot be obtained. There is a limit to the upper limit of rotation speed. In addition, when the rotation speed of the magnetic developing roll is made variable, a density difference occurs between the leading edge and trailing edge of a copied image (especially wide lines or characters) in the developing direction, that is, in the direction of movement of the photoreceptor relative to the developing device. It's getting better.

In method (2), even if the surface potential of the photoreceptor is kept constant and the potential of the developing bias is varied, the range of variation in the density of the line image is small due to the presence of edge effects, while the density variation of the fin image and solid Since the density change of the image varies greatly depending on the fluctuation of the potential of the developing bias, it is not possible to obtain a stable copied image. For example, when reversal development is performed as in a laser beam printer, to explain in detail, a line image is developed mainly based on the edge effect, and the development density is Vo-Vi (Vo:g charged potential on the surface of the light body, ■i : Determined in proportion to the surface potential of the image area). On the other hand, solid images are developed mainly based on electrode effects, and the developed density is VB-Vt (vB
: Determined in proportion to development bias potential). therefore,
Even if the potential of the developing bias is varied, the above-mentioned problem still occurs.

Purpose The present invention has been made in view of the above-mentioned problems, and an object thereof is to increase the density variable width of a line image and to improve a fin image. An object of the present invention is to provide an electrophotographic copying machine that can adjust the density of a copied image while keeping the density change of a solid image and the density change of a solid image substantially constant.

SUMMARY In order to achieve the above objects, the present invention provides that at least either the electric power supplied to the charging means or the potential applied to the developing bias to the developing electrode can be adjusted, and when this is adjusted, the charging means The apparatus is provided with means for controlling the charging potential on the surface of the photoreceptor in association with the potential applied to the developing electrode by the developing bias applying means.

Embodiment FIGS. 1 and 2 show a first embodiment of an electrophotographic copying machine according to the present invention.

(11jlE photoreceptor dome, which has an As2Se3 photoreceptor deposited on the surface of an aluminum drum, and can be rotated counterclockwise in Fig. 1 at a circumferential speed of 170 m/sec. (2) is an electrostatic charger. , (3) is a charging power source, and the charging charger (2) charges the surface of the photoreceptor drum (1) to medium polarity using medium polarity power supplied from the power source (3). (4) is a charging power source. The potential detector is installed adjacent to the charger (2) and detects the surface potential of the photosensitive drum (11) immediately after being charged by the charger (2).

(5) is a laser beam irradiation mechanism that irradiates only the image area with a laser beam at an irradiation amount (unchanged) of 1.0 μJ/cd-sec. The image is a black and white pattern without halftones, and the surface potential of the photosensitive drum (1) in the irradiated area is attenuated to about 25V.

(6) is a magnetic brush type developing device, which includes a developing sleeve (8) with a built-in magnetic roll (7).
is magnetized with 8 poles in the circumferential direction, and 1 in the counterclockwise direction in Figure 1.
It can be rotated at 00 Orpm. Developing sleeve (
8) has an outer diameter of 31 groups, with 2 or
It can be rotated at pm. As a developer, 94W [%
A mixture of small diameter magnetic carrier and 6 wt% insulating toner is used. The small-diameter magnetic carrier is made by dispersing magnetic fine powder in resin, and has an average particle size of 21 μm and a resistance of 10.
14Ωα, and the frictional charging polarity with respect to the toner is ←).

The toner is insulative and non-magnetic, has an average particle size of 11 μm, and has medium frictional polarity with respect to the carrier. This developer is formed into a magnetic brush on the outer peripheral surface of the developing sleeve (8) by the magnetic force of the magnetic roll (7), and is exclusively applied to the magnetic roll ('7).
The developing sleeve (8) is conveyed clockwise based on the rotation of the developing sleeve (8), and the electrostatic latent image formed on the photosensitive drum (1) is reversely developed. That is, the toner charged in peaks is irradiated with approximately 25V by the laser beam irradiation mechanism (5).
It attaches to the image area that has been attenuated. In this case, the development gap is 0.7 m+. Further, the developing sleeve (8)
A developing bias of medium polarity is applied from the developing bias power supply (9), and functions as a developing electrode.

01) is (transfer charger that performs medium polarity corona discharge,
0 is an AC charger for separating copy paper, 03 is a residual toner cleaning blade, 0→ is a main eraser lamp, OQ is a sub charger that performs medium polarity corona discharge, 0'I) is a sub eraser lamp. be.

On the other hand, (10) is a control circuit that adjusts the image density, and controls the charging potential on the photoreceptor drum (1) as well as the developing bias potential, and the potential applied to the developing tube is controlled by the detector. Based on the charged potential of the photosensitive drum (1) fed back in (4), VB = Vo
200 (2) - (2) VB =Developing bias potential (200): Determined to satisfy the relationship of photoreceptor charging potential (200).

Specifically, when the image density adjustment knob 0υ provided on the operation panel shown in Figure 2 is manually operated, the resistance value of the variable resistor installed in the four parts changes accordingly, and the resistance value changes depending on this change in resistance value. The power supply to the charger (2) is adjusted accordingly. In this case, the closer the knob 0Q is to the scale "1", the darker the image density becomes; when the scale matches "1", the charging potential is 450■, and when it matches the scale "1", the charging potential is 350■, When it matches the scale "5", it is adjusted to 250■.

The charged potential on the photoreceptor drum (1) adjusted in this way and attached by the charger (2) is detected by the detector (4), and is determined by the control circuit (10) based on the above equation 0. A developing voltage having a potential value determined by the voltage is applied from the power source (9) to the developing sleeve (8). That is, the charging potential is 450
If ■, the developing bias potential is 250■, B 50V"
r, f) tlJfl OOV, 250Vte, lLha5
The absolute value of the potential difference between the charging potential and the developing Ianu potential is maintained at 200V.

FIG. 3 is a graph showing changes in image density when the charging potential (Vo) is varied in the range of 250 to 450 in this first embodiment, and the horizontal axis represents the development bias potential (VB). varies in the range of 50 to 250 V based on the above formula 0. The Graph 79947 image was measured by copying a 0.5 width fin image, and the solid image was measured at the center of a 5×51 solid image.

FIG. 4 shows the copying machine shown in FIG. 1 in which the charging potential (Vo) is fixed at 450 cm, while the developing bias potential (VB) is
It is a graph as a comparative example showing the change in image density when varying it in the range of 50 to 250 square meters.

As is clear from these two graphs, the density variation width of the fin image in FIG. 3 according to the present invention is larger, and it approximates the density change characteristic curve of a solid image, and even when the developing bias potential fluctuates, there is no line. The density change of the image and the density change of the solid image are maintained substantially constant. The reason why the density variation width of the fin image increases is the potential difference between the charging potential (vO) on the surface of the photoreceptor and the developing bias potential (VB) +
This is because by keeping Vo −VB + constant, the development itself based on the edge effect will also be affected. Furthermore, it is advantageous to keep the potential difference +Vo -VB + constant because it prevents fog from occurring due to image density adjustment.

In this first embodiment, the detection of the charging potential by the detector (4) is omitted, and the developing bias is adjusted in response to the change in resistance value (selection of the charging potential (■0)) by operating the knob 00. The potential (VB) may be automatically adjusted by the control circuit 00.

Next, a second example will be described. This second embodiment basically uses the same device as shown in FIG. 1 except for the control circuit (10), and instead of the image density adjustment knob 00 shown in FIG. It is equipped with an operation panel and three selection switches for the 9 wheels.

Then, this selection switch (I(l.

When either M or (I-1') is turned on, the control circuit (10) predetermines that the potential difference between the charging potential (Vo) and the developing bias potential (VB) maintains six substantially constant values. Charger (2)
Similarly, a developing bias having a predetermined potential value is applied to the developing sleeve (8). In this embodiment, the charged potential detected by the detector (4) is fed back to the control circuit (10) and compared with a reference potential stored in the control circuit (10), so that the charged potential is determined in advance. The power supplied to the charger (2) is finely adjusted so that it reaches a predetermined value.

Specifically, in the above embodiment, each selection n, M
1, (When I-1 is turned on, the electric power and development potential (V
B) is supplied and applied to the electrification charger (2) and the developing sleeve (8).

Note that in this second embodiment, the charger (2)
When either the power supplied to the developing sleeve (8) or the potential applied to the developing sleeve (8) is adjusted to increase, specifically when the selection switch is switched from (c) to open,
The absolute value of the potential difference is slightly increased from 225V to 250V. To do this, the photoreceptor drum (1
This is done in consideration of the fact that charging unevenness on the surface of () becomes more noticeable as the charging potential increases, causing fog in the developed image. That is, by doing so, the occurrence of the above-mentioned fog can be effectively prevented.

In addition, the above-mentioned No. 1. In the second embodiment, the charging potential (■0
) is preferably 700■ or less, and the potential difference is 1V.

-VBl is preferably in the range of 25 to 300 . This is because in the above embodiment, the charging potential (■0) is 700
If it exceeds ■, uneven fogging is likely to occur in the developed image.
This is because if the potential difference IVo-VBI exceeds 300V, carriers will adhere to the non-image area, and if it is below 25V, fog will occur in the developed image.

Effects As is clear from the above explanation, the present invention provides that at least either the power supplied to the charging means or the potential applied to the developing electrode can be adjusted, and when this is adjusted, the charging means Since the device is provided with a means for controlling the charging potential on the surface of the photoreceptor in relation to the potential applied to the developing electrode by the developing voltage applying means, it is possible to widen the range of variation in the density of the line image. As a result, the density change characteristic curve of the fin image approximates that of the solid image, and even if the potential value of the developing bias changes, the density change of the line image and the density change of the solid image are approximately constant, making it stable. A duplicate image can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an electrophotographic copying machine according to the present invention, FIG. 2 is a plan view of its operation panel, FIG. 3 is a graph showing changes in image density according to the present invention, and FIG. 4 is an image according to a comparative example. It is a graph showing changes in concentration. (11... Photosensitive drum, (2)... Charger, (3)... Charger power supply, (4)...
Charged potential detector, (5)...laser beam irradiation mechanism,
(6)...Developing device, (8) 10. Developing sleeve, (9)...Developing bias power supply, (10)...Control circuit, 00...Image density adjustment knob. Patent applicant Minolta Camera Co., Ltd. Agent
Patent attorney Maeda Ao and 2 others Figure 2 @ Sutaku 1 @ Shocking

Claims (1)

[Claims] (11) An electrophotographic photoreceptor, a means for uniformly charging the surface of the photoreceptor, a means for supplying power to the charging means, and a means for irradiating light onto the uniformly charged surface of the photoreceptor. an electrophotographic copying apparatus, comprising means for forming an electrostatic latent image on the surface thereof, a means for developing the electrostatic latent image while having a developing electrode, and means for applying a developing bias to the developing electrode. In the machine, at least either the power supplied to the charging means or the potential applied to the developing electrode can be adjusted, and when this is adjusted,
An electrophotographic copying machine characterized by comprising means for correlating and controlling the charging potential of the surface of the photoreceptor charged by the charging means and the potential applied to the developing electrode by the developing bias applying means.